1. The Field of the Invention
The present invention relates generally to optical transceivers. More specifically, the present invention relates to optical transceivers that use microcode to perform self-calibration to environmental conditions.
2. Background and Relevant Art
Computing and networking technology have transformed our world. As the amount of information communicated over networks has increased, high speed transmission has become ever more critical. Many high speed data transmission networks rely on optical transceivers and similar devices for facilitating transmission and reception of digital data embodied in the form of optical signals over optical fibers. Optical networks are thus found in a wide variety of high speed applications ranging from as modest as a small Local Area Network (LAN) to as grandiose as the backbone of the Internet.
Typically, data transmission in such networks is implemented by way of an optical transmitter (also referred to as an electro-optic transducer), such as a laser or Light Emitting Diode (LED). The electro-optic transducer emits light when current is passed through it, the intensity of the emitted light being a function of the current magnitude. Data reception is generally implemented by way of an optical receiver (also referred to as an optoelectronic transducer), an example of which is a photodiode. The optoelectronic transducer receives light and generates a current, the magnitude of the generated current being a function of the intensity of the received light.
Various other components are also employed by the optical transceiver to aid in the control of the optical transmit and receive components, as well as the processing of various data and other signals. For example, such optical transceivers typically include a driver (e.g., referred to as a “laser driver” when used to drive a laser signal) configured to control the operation of the optical transmitter in response to various control inputs. The optical transceiver also generally includes an amplifier (e.g., often referred to as a “post-amplifier”) configured to amplify the channel-attenuated received signal prior to further processing. A controller circuit (hereinafter referred to the “controller”) controls the operation of the laser driver and post-amplifier.
The operation of optical transceiver is susceptible to its operating environment. For example, temperature can change the operating characteristics of the optical transmitter itself. In particular, the wavelength output of a laser may drift from approximately 0.3 nanometers (nm) to approximately 0.6 nm for every one degree Celsius change in temperature. Since lasers generate heat during operation, this can have a significant effect upon the operation of the laser. Wavelength variations can cause crosstalk, where one transmission becomes confused with another. Furthermore, varying wavelengths due to varying laser temperature may cause different fiber attenuations. Accordingly, temperature has great influence over the proper operation of the optical transceiver.
Some high performance optical transceivers include a Thermo Electric Cooler (TEC) which cools or heats the optical transceiver as appropriate to counteract the heating or cooling effect of the surrounding environment. However, even with such countermeasures, there is still some variance in temperature of the laser itself. In order to further improve the performance of the laser, the laser bias current may be adjusted to further counteract the effects of temperature on the operating wavelength of the laser.
The transmitter itself (e.g., the laser) may have some uncertainty in its operating performance due to the inherent variances in semiconductor processing technologies. Even lasers of the same type having undergone the same manufacturing processes may have different temperature/laser bias current dependencies. Accordingly, it is often necessary for high performance and high speed applications, to individually calibrate each optical transceiver with a temperature/laser bias current table. The optical transceiver then refers to the table when deciding what laser bias current magnitude to bias the laser with given the current temperature.
This calibration can take significant amount of human effort, thereby increasing the cost of the optical transceiver as a whole. Therefore, what would be desired is an optical transceiver that calibrates without requiring excessive human intervention.